Concrete block is a reliable building material

Q. I'm building a new home, and two concrete block piers toppled over when a ladder was leaned against one. The one pier crashed into the second one. Why did this happen and what could have prevented it? I thought concrete block was the smart product to use for my foundation and home, but now I wonder if I made a big mistake. Have you built with concrete block successfully? What did you do?

A. Let's start out by reassuring you that concrete block is a great building material. It's strong, it can be used in any number of ways, and it is used in all sorts of residential, commercial and industrial applications.

Stop second-guessing yourself. You need to direct that attention to the contractor on your job and any written specifications that were part of your blueprints and plans.

The block piers toppled over because the connection between the mortar and the concrete block is not able to resist the force of being pulled apart. The ladder placed against the top of the pier converted the pier to a lever. The seemingly minimal force at the top of the ladder was multiplied at the base of the pier where it fractured.

The vast majority of concrete blocks are hollow. When laid on their side and stacked in an offset manner, they somewhat resemble a honeycomb made by a hive of bees. Bees fill the void spaces of the honeycomb with honey. Your contractor should have filled the hollow spaces in the block with pea gravel concrete and steel bars.

Realize that he may have been getting ready to do this just before the accident occurred. Someone may have goofed up and put sideways pressure on the pier before the concrete and steel could be added.

Concrete, mortar and almost all rock are very strong when you compress them, but these materials usually only have 1/10 the strength when you try to bend or stretch them. Engineers and technical folk call those bending or stretching forces tension.

Steel has fantastic tensile strength. For example, common 1/2-inch reinforcing steel on a residential job site may be rated at 40,000 pounds of tensile strength. That means it fails or tears apart once you apply 40,000 pounds of pulling force to it.

Once your contractor mixes up small pea gravel concrete — not the sandy mortar he used to lay the block — and pours it into the block voids along with the long steel rods, the concrete block then starts to resemble reinforced poured concrete.

It's a best practice to use this same reinforcing steel to connect the concrete block walls to the poured concrete footer. I did this on all my jobs, making sure the steel rods protruded up from the concrete footer about 2 feet. I then dropped the long steel bars from above down to the top of the footer so the steel pieces overlapped.

The reason you want to use the pea gravel concrete instead of mortar is that it's stronger. The rocks used in concrete mixes are responsible for much of the strength concrete achieves once it's cured. It's important that the steel bars in the block are centered in the void spaces to ensure they're surrounded by concrete.

You can also used thin wire reinforcing for concrete block walls. This unique product is placed on top of a row of block in the horizontal mortar joints. This thin steel, once embedded in the mortar, adds significant strength to long concrete block walls.

Pilasters or wide piers can also be incorporated into long and tall concrete block walls to add more strength. Once again, it's best to have a structural engineer specify where and how these elements should be incorporated into your design.

One of the things I really like about concrete block is that the average person can build with it. You can use decorative concrete block around your home for all sorts of projects. Just be sure you reinforce it if you want it to stand the test of time.

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